Portable traffic control apparatus of the trailer type having an arrow display panel thereon is well known in the art. These traffic control devices are trailer mounted, self-powered devices that may be moved from location to location for signalling traffic. These types of traffic controllers are usually used for warning as to hazardous construction areas or maintenance zones, or in high density or high speed traffic zones, to give the drivers of motor vehicles approaching such areas or zones advance warning thereof. The traffic controller is mounted at a sufficient height from the road surface to be clearly visible to an approaching driver of a motor vehicle and sufficiently in advance of the traffic condition to be avoided to permit the driver to assimilate the directions signalled by the traffic arrow panel so that the driver can take the necessary corrective action in sufficient time to avoid the undesirable traffic condition. These types of devices are known in the art as advance warning flashing arrow panels and must conform to the requirements of Part 6E-7, "Advance Warning Flashing Arrow Panels", of the Federal Highway Administration's Manual of Uniform Traffic Control Devices.
Most the the present day advance warning trailer mounted traffic control apparatus is basically similar in design. Basically, all of the trailer mounted prior art advance warning traffic control apparatus have a very large arrow panel for providing traffic control direction by means of electrical lights that are controlled to define various traffic control directions, such as, for example, a flashing directional arrow. The trailer mounted display panels range in size from 48 inches by 96 inches, and 36 inches by 72 inches, and weigh on the order of 150 pounds. All of the prior art apparatus has some means for moving these heavy panels between a display position for traffic control and a storage position for transit to permit the trailer to be readily transported to a new location requiring traffic control. Typical prior art traffic control apparatus are disclosed in U.S. Pat. Nos. 3,622,980; 3,886,519; 4,077,144; 4,087,785 and Des. 234,754.
These prior art devices for controlling the positions of the traffic control display panels include winch and cable assemblies, telescoping and rotating tube type masts, hydraulic lifting mechanisms, or the like. In addition, lifting and lowering devices for other purposes are exemplified by U.S. Pat. Nos. 2,815,132; 2,964,122; 3,545,243; 1,162,413 and 547,077. None of these prior art mechanisms for moving a traffic control display panel between a display position and a storage position for transit is completely satisfactory. In addition to the problems associated with the actual use of the trailer mounted traffic control apparatus, the heavy trailer mounted traffic control apparatus are expensive to ship from the point of manufacture to the ultimate user because they are large, bulky, heavy and difficult to handle. In one particular prior art trailer mounted traffic control apparatus, in order to reduce the expense of shipment of such trailers, a technique was devised to permit the stacking of a pair of trailers, one on top of another, to increase or double the number of trailers that could be shipped in a truck trailer or similar shipping compartment. In order to stack the trailers in this fashion, it was necessary to remove the traffic arrow panel from the trailer from the supporting structure and then diassemble the structural components for mounting the traffic control arrow panel in a traffic display position in preparation for stacking of the trailers. Once the traffic control trailers are disassembled in this fashion, they can be stacked one on top of another. The disassembled structural components can then be stacked and secured together on the topmost stacked trailer. The traffic message panel is also removed and is shipped in a separate cardboard carton for protective purposes. Upon receipt of the stacked trailers at the point of destination, it was necessary to unstack the trailers and reassemble the structural components on the trailer in preparation for mounting the arrow panel. One of the most difficult tasks with such a prior art trailer mounted traffic control apparatus was to secure the message panel in the display position, since the panel weighs about 150 pounds, they had to be hoisted by two persons about 8 feet above the supporting surface in order to render the trailer usable. Accordingly, there is a present need for a portable traffic control device of the trailer mounted type having an improved lifting and lowering apparatus that can be readily operated for lifting the traffic arrow panel to a preselected display position and lowering the traffic arrow panel to a storage position for local transit. In addition, the improved trailer mounted traffic control apparatus should be designed to permit double stacking of trailers without requiring dismantling of the lifting/lowering control linkage for the display panel, prior to stacking, for shipping the trailers from the manufacturing site.